Leases - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Jan. 01, 2019
Lessee Lease Description [Line Items]
Operating lease, option to extend			true
Deferred rent	$ 1.5		$ 1.5
Lease assets	$ 25.3		$ 25.3
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	us-gaap:OtherNoncurrentAssetsMember		us-gaap:OtherNoncurrentAssetsMember
Short-term lease liabilities	$ 9.6		$ 9.6
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:AccruedLiabilitiesAndOtherLiabilities		us-gaap:AccruedLiabilitiesAndOtherLiabilities
Long-term lease liabilities	$ 17.2		$ 17.2
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	us-gaap:OtherLiabilitiesNoncurrent		us-gaap:OtherLiabilitiesNoncurrent
Operating lease rent expense	$ 2.6	$ 1.9	$ 7.4	$ 5.5
Cash paid of measurement of operating lease liabilities	$ 2.7		$ 7.4
Weighted average discount rate of operating leases	4.10%		4.10%
Average remaining operating lease term	2 years 9 months 18 days		2 years 9 months 18 days
Operating lease liabilities, lease not yet commenced	$ 5.0		$ 5.0
Minimum [Member]
Lessee Lease Description [Line Items]
Operating lease expiration year			2019
Maximum [Member]
Lessee Lease Description [Line Items]
Operating lease expiration year			2025
Operating lease option to extend lease term			five years
Accounting Standards Update 2016-02 [Member]
Lessee Lease Description [Line Items]
Estimated operating lease assets and liabilities to be recognized upon adoption					$ 21.6